Abstract
Foodborne infections with enterohemorrhagic Escherichia coli (EHEC) are a major cause of diarrheal illness in humans and can lead to severe complications such as hemolytic uremic syndrome. Cattle and other ruminants are the main reservoir of EHEC, which enters the food chain through contaminated meat, dairy, or vegetables. Here, we describe the establishment of a vertebrate model for foodborne EHEC infection, using larval zebrafish (Danio rerio) as a host and the protozoan prey Paramecium caudatum as a vehicle. We follow pathogen release from the vehicle, intestinal colonization, microbe-host interactions, and microbial gene induction within a live vertebrate host, in real time, throughout the course of infection. We demonstrate that foodborne EHEC colonizes the gastrointestinal tract faster and establishes a higher burden than waterborne infection. Expression of the locus of enterocyte effacement (LEE), a key EHEC virulence factor, was observed early during infection, mainly at sites that experience fluid shear, and required tight control to enable successful host colonization. EHEC infection led to strain- and LEE-dependent mortality in the zebrafish host. Despite the presence of the endogenous microbiota limiting EHEC colonization levels, EHEC colonization and virulence can be studied either under gnotobiotic conditions or against the backdrop of an endogenous (and variable) host microbiota. Finally, we show that the model can be used for investigation of factors affecting shedding and transmission of bacteria to naive hosts. Overall, this constitutes a useful model, which ideally complements the strengths of existing EHEC vertebrate models. IMPORTANCE Enterohemorrhagic Escherichia coli (EHEC) is a foodborne pathogen which can cause diarrhea, vomiting, and, in some cases, severe complications such as kidney failure in humans. Up to 30% of cattle are colonized with EHEC, which can enter the food chain through contaminated meat, dairy, and vegetables. In order to control infections and stop transmission, it is important to understand what factors allow EHEC to colonize its hosts, cause virulence, and aid transmission. Since this cannot be systematically studied in humans, it is important to develop animal models of infection and transmission. We developed a model which allows us to study foodborne infection in zebrafish, a vertebrate host that is transparent and genetically tractable. Our results show that foodborne infection is more efficient than waterborne infection and that the locus of enterocyte effacement is a key virulence determinant in the zebrafish model. It is induced early during infection, and loss of tight LEE regulation leads to a decreased bacterial burden and decreased host mortality. Overall, the zebrafish model allows us to study foodborne infection, including pathogen release from the food vehicle and gene regulation and its context of host-microbe interactions, as well as environmental shedding and transmission to naive hosts.
Highlights
Foodborne infections with enterohemorrhagic Escherichia coli (EHEC) are a major cause of diarrheal illness in humans and can lead to severe complications such as hemolytic uremic syndrome
We studied the interactions between P. caudatum and the enterohemorrhagic E. coli O157:H7 Sakai strain to establish if and for how long bacteria would persist within Paramecium
Fluorescence imaging following coculture with EHEC::mCherry revealed that the paramecia contained E. coli, which was localized within food vacuoles (Fig. 1B to D)
Summary
Foodborne infections with enterohemorrhagic Escherichia coli (EHEC) are a major cause of diarrheal illness in humans and can lead to severe complications such as hemolytic uremic syndrome. In order to control infections and stop transmission, it is important to understand what factors allow EHEC to colonize its hosts, cause virulence, and aid transmission Since this cannot be systematically studied in humans, it is important to develop animal models of infection and transmission. Our results show that foodborne infection is more efficient than waterborne infection and that the locus of enterocyte effacement is a key virulence determinant in the zebrafish model It is induced early during infection, and loss of tight LEE regulation leads to a decreased bacterial burden and decreased host mortality. Ongoing studies of EHEC focus on understanding how the LEE is regulated during the EHEC life cycle and how the LEE-carried genes and other virulence factors, such as Shiga toxin (Stx), contribute to colonization, disease pathogenesis, and transmission Another area of interest is how a host’s endogenous microbiota interacts with EHEC and how this affects host fate following EHEC ingestion. It is technically challenging to study host-microbe interactions at the single-cell level in this context
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